Compact UV Laser for Fusion Diagnostics

The neutral density in magnetically confined fusion experiments is an important parameter, affecting plasma stability and confinement and providing fuel for the plasma. Despite this importance, few diagnostics exist to directly measure the neutral density. One diagnostic is two-photon absorption laser induced fluorescence (TALIF). Current TALIF systems rely on large, dye laser based systems to produce deep UV (DUV) laser light. Such lasers pose a number of issues that prevents their use on fusion experiments. We propose to design and construction of a compact, solid-state UV laser to replace dye lasers in TALIF system. The laser light will be produced through harmonic frequency generation of the fundamental of a solid-state pumped Yb:YAG laser. In Phase I we will demonstrate that by using a series of non-linear crystals we can produce 206 nm light, the fifth harmonic frequency of the Yb:YAG laser. We will demonstrate that the fundamental of the Yb:YAG laser can be tuned to 1025 nm while maintaining high output energy. We will produce a conceptual design a high energy version of the system for Phase II, capable of producing a sufficient signal-to-noise ratio in a working magnetically confined fusion experiment. In Phase II we will build the laser system to be installed on a magnetic fusion experiment to measure the neutral density in the edge region. Such as diagnostic can be applied to any plasma device where the neutral density is an important parameter, aiding in control of plasma experiments from fusion devices to plasma processing devices. A compact UV laser would also be useful for other diagnostic systems, specifically Raman scattering, where such a laser would increase signal levels while operating far from bright background sources.